Catalysis of “outer-phase” oxygen atom exchange reactions by encapsulated “inner-phase” water in {V(15)Sb(6)}-type polyoxovanadates

Antimonato polyoxovanadate (POV) cluster compounds {M(en)(3)}(3)[V(15)Sb(6)O(42)(H(2)O)(x)]·nH(2)O (M = Fe(II), Co(II), Ni(II) and x = 0 or 1) obtained under solvothermal conditions exhibit unusual high water solubility making these compounds promising synthons for generation of new POV structure types. Electrospray ionization mass spectrometry provides evidence (i) for a water molecule encapsulated inside the cavity of a fraction of the spherical cluster shells, (ii) for a post-functionalization in water, namely a slow exchange of VO against Sb(2)O, (iii) for the inner-phase reactivity of the encapsulated water that is capable of opening an oxo-bridge, and (iv) for a significant acceleration of the (16)O/(18)O exchange reactions of oxygen atoms in the cluster periphery with surrounding H(2)(18)O, when encapsulated water is present. To the best of our knowledge, this is the first example in polyoxovanadate chemistry for the transduction of inner-phase reactivity of an encapsulated guest molecule into changes in the outer-phase reactivity of the cluster. Magnetic susceptibility measurements reflect the individual contributions of the frustrated {V(15)} spin polytope and the {M(en)(3)}(2+) complexes, with very weak coupling between these groups.